Early detection and subsequent treatment of breast cancer can have a significant impact on improving the length and quality of life of those afflicted with this disease. Approximately eighty million women should receive annual screening for breast cancer. In actual fact, approximately twenty-five million breast cancer mammograms are performed annually in the U.S. Most of the mammograms are performed with X-ray technology. Of the women screened, the initial mammograms identify some 2,300,000 women as having a suspicious breast mass. Follow-up mammogram diagnosis, again by X-ray mammogram, identifies some 165,000 women as having a tumor; biopsies are then conducted to determine whether the tumor is malignant or benign. The biopsies identify about 41,000 malignant tumors.
Two major problems exist. One is false negatives that are found during the initial X-ray mammogram screening exam. According to the Federal Food and Drug Administration (xe2x80x9cFDAxe2x80x9d), screening mammography examinations fail to detect some 11,500 malignant tumors [false negatives]. During the mammography diagnostic exams, some 4,400 additional malignant tumors are not detected. The result is that some 16,000 women who have been examined may have a malignant tumor and not know it.
The second major problem is false positives. The X-ray mammography screening process will show some 2,260,000 false positives [indications of suspicious masses]. Those patients with suspicious masses, according to the FDA, may next undergo a diagnostic mammography exam; this procedure may generate 165,000 positive indications. Up to 165,000 biopsies are needed to determine which of the identified tumors are malignant and which are benign. Of this number, the biopsies will show about 125,000 are false positive [benign tumors] and 40,000 are true positive [malignant tumors]. The biopsies are costly; moreover, they introduce anxiety and uncertainty for the patients.
A number of conventional technologies have been proposed to help resolve benign tumors from malignant tumors. Ultrasound and MRI are both used for this purpose. However, ultrasound equipment is expensive and is currently approved to characterize the malignancy of only the larger tumors. MRI equipment is even more expensive and may often require injection of a contrast agent. Other methods sense tumor-induced low-frequency potentials or impedance changes on the surface of the breast. Such methods have been clinically tested but have failed thus far to obtain FDA approval. Sensing tumor-induced infrared emission from the surface of the breast is also being studied. However, past clinical trials with the infrared method have not proved promising.
Methods and apparatus have been considered to characterize tissues, especially to detect or image breast cancers. These are described in U.S. Pat. No. 5,704,355, issued to Jack E. Bridges and entitled xe2x80x9cNon Invasive System for Breast Cancer Detectionxe2x80x9d and in two pending patent applications of Jack E. Bridges entitled xe2x80x9cMicrowave Method to Detect and System to Detect and Locate Cancer in Heterogeneous Tissuesxe2x80x9d, U.S. Ser. No. 08/641,834, now U.S. Pat. No. 5,829,437 and xe2x80x9cBreast Cancer Detection, Imaging and Screening by Electromagnetic Millimeter Wavesxe2x80x9d, U.S. Ser. No. 08/843,858 now U.S. Pat. No. 5,807,257. The technology described in the aforesaid patent, and in the aforesaid pending patent applications, is incorporated by reference in this application.
One objective of this patent application is to describe improvements in the above noted patent and pending applications that will characterize the differences between malignant and benign tumors. A second objective is to describe techniques that will detect the vascularization that indicates the presence of an incipient malignant tumor, however tiny it may be.
The above-noted microwave technology contrasts tissues based primarily on electrical characteristics determined at least in part by their water content. The differing water content between normal and malignant breast tissues results in an order of magnitude increase in the scattering characteristics of a tumor relative to normal breast tissue. Thus microwave method xe2x80x9cseesxe2x80x9d the entire tumor, because the tumor has a high water content. In the case of X-ray mammography, the scattering cross-sections are much smaller than for microwave examination. X-ray mammography often can detect a malignant tumor only if micro calcifications are present. Likewise, ultrasound equipment suffers from a lack of contrast between different (malignant of benign) soft tissues.
Similarly, a single antenna may be moved over the breast to create a synthetic aperture array. Such an array can produce signals which, when properly processed, can detect and/or image a tumor.
Other high water content tissues may also be detected or imaged by any of the above-noted systems. For example, some but not all benign tumors can also have a substantial water content. Muscle tissue and arteries, veins and capillaries can also have a high water content. These tissues may also be either detected or imaged by the above-noted microwave system.
As described in the above-noted Bridges patent and pending applications, the functions of detection and imaging can be enhanced by use of differences in the back, forward, and side scatter polarization effects and spectral responses. Not described is how these responses can be used to discriminate malignant from benign tissue. Also not described is how other tumor related phenomena, such as angiogenesis, can be exploited, not only to characterize the nature of a sensed or imaged tumor, but also to help detect the vascularization that indicates the presence of tiny incipient malignant tumors. Further, the need to develop data on the tissues near a tumor, and especially between the tumor and adjacent blood vessels, is not fully discussed.
It therefore is an object of this invention to show how the system and methods of the above-noted patent and pending applications of Bridges can be improved and applied to characterize the nature of tumors and to enhance the detectability of very small tumors. The methods and apparatus described in the Bridges patent and pending applications can be used to characterize geometric features unique to malignant tumors. These are based on (1) geometric differences between benign and malignant tumors, (2) the presence of capillaries in the tissue near a malignant tumor, and (3) the presence of a network of capillaries, tiny veins and perhaps an artery between the malignant tumor and major blood supply vessels. The method, as well as the apparatus, can be further modified to characterize or image the tissues surrounding a possible tumor, especially the tissues between a possible tumor and a small vein or artery.